Weird sound in the cooling system when I turn off the engine on 2007 Mercedes-Benz GL450

I bought the car a few weeks ago and didn't notice it until a couple of days ago. When I turn off the engine, after a few seconds I hear a "ffffffff" sound. like if it was releasing some kind of pressure. Any one has any idea of what it could be???
Thanks.

Asked by for the 2007 Mercedes-Benz GL450
1 answer 1 comment
This sounds like it is the airmatic sytem that is releasing air from the air suspension. It's normal.
Thanks so much for your answer. What a relief :)